diff --git a/core/tests/Drupal/Tests/Core/Cache/Context/QueryArgsCacheContextTest.php b/core/tests/Drupal/Tests/Core/Cache/Context/QueryArgsCacheContextTest.php
index 93a11c5..3e13b23 100644
--- a/core/tests/Drupal/Tests/Core/Cache/Context/QueryArgsCacheContextTest.php
+++ b/core/tests/Drupal/Tests/Core/Cache/Context/QueryArgsCacheContextTest.php
@@ -31,15 +31,15 @@ public function testGetContext(array $query_args, $cache_context_parameter, $con
    */
   public function providerTestGetContext() {
     return [
-      [[], NULL, NULL],
-      [[], 'foo', NULL],
+      [[], NULL, ''],
+      [[], 'foo', ''],
       // Non-empty query arguments.
       [['llama' => 'rocks', 'alpaca' => '', 'panda' => 'drools', 'z' => '0'], NULL, 'alpaca=&llama=rocks&panda=drools&z=0'],
       [['llama' => 'rocks', 'alpaca' => '', 'panda' => 'drools', 'z' => '0'], 'llama', 'rocks'],
       [['llama' => 'rocks', 'alpaca' => '', 'panda' => 'drools', 'z' => '0'], 'alpaca', '?valueless?'],
       [['llama' => 'rocks', 'alpaca' => '', 'panda' => 'drools', 'z' => '0'], 'panda', 'drools'],
       [['llama' => 'rocks', 'alpaca' => '', 'panda' => 'drools', 'z' => '0'], 'z', '0'],
-      [['llama' => 'rocks', 'alpaca' => '', 'panda' => 'drools', 'z' => '0'], 'chicken', NULL],
+      [['llama' => 'rocks', 'alpaca' => '', 'panda' => 'drools', 'z' => '0'], 'chicken', ''],
     ];
   }